System and method for supporting operations of advanced power over ethernet system

ABSTRACT

A Power over Ethernet (PoE) system having a Power Sourcing Equipment (PSE) and a Powered Device (PD) configured for interacting over four pairs of wire provided for supplying power from the PSE to the PD. The PSE and the PD are configured to perform separate PD classification procedures over first and second 2-pair sets to support PoE operations that are not defined by the IEEE 802.3af standard.

TECHNICAL FIELD

This disclosure relates to power supply systems, and more particularly, to circuitries and methodologies for supporting operations of a Power over Ethernet (PoE) system.

BACKGROUND ART

Over the years, Ethernet has become the most commonly used method for local area networking. The IEEE 802.3 group, the originator of the Ethernet standard, has developed an extension to the standard, known as IEEE 802.3af, that defines supplying power over Ethernet cabling. The IEEE 802.3af standard defines a Power over Ethernet (PoE) system that involves delivering power over unshielded twisted-pair wiring from Power Sourcing Equipment (PSE) to a Powered Device (PD) located at opposite sides of a link. Traditionally, network devices such as IP phones, wireless LAN access points, personal computers and Web cameras, have required two connections: one to a LAN and another to a power supply system. The PoE system eliminates the need for additional outlets and wiring to supply power to network devices. Instead, power is supplied over Ethernet cabling used for data transmission.

As defined in the IEEE 802.3af standard, PSE and PD are non-data entities allowing network devices to supply and draw power using the same generic cabling as is used for data transmission. A PSE is the equipment electrically specified at the point of the physical connection to the cabling, that provides the power to a link. A PSE is typically associated with an Ethernet switch, router, hub or other network switching equipment or midspan device. A PD is a device that is either drawing power or requesting power. PDs may be associated with such devices as digital IP telephones, wireless network access points, PDA or notebook computer docking stations, cell phone chargers and HVAC thermostats.

PSE's main functions are to search the link for a PD requesting power, optionally classify the PD, supply power to the link if a PD is detected, monitor the power on the link, and disconnect power when it is no longer requested or required. A PD participates in the PD detection procedure by presenting detection and classification signatures to request power and indicate its power level class. The PD detection signature has electrical characteristics measured by the PSE.

Recent developments of advanced PoE-related products create need for new systems and methodologies for supporting advanced PoE operations.

SUMMARY OF THE DISCLOSURE

The Summary is segmented by specific aspects of the disclosure.

In accordance with a first aspect of the disclosure, an advanced PoE system comprises an advanced PSE and an advanced PD linked by a first 2-pair set of wires and a second 2-pair set of wires. The PSE and the PD are configured to perform first classification of the PD over the first set, followed by second classification of the PD performed over the second set. The PD is configured to present a class during the second classification the same as or different from the class presented during the first classification.

In accordance with a second aspect of the disclosure, an advanced PoE system comprises an advanced PSE and an advanced PD linked by a first 2-pair set of wires and a second 2-pair set of wires. After the PD is classified over the first 2-pair set, the PD changes its class on the first 2-pair set as classification is performed over the second 2-pair set.

In accordance with a third aspect of the disclosure, an advanced PoE system comprises an advanced PSE and an advanced PD linked by a first 2-pair set of wires and a second 2-pair set of wires. The PSE and the PD are configured to perform first classification of the PD over the first set, followed by second classification of the PD performed over the second set. The PD is configured to present during a further classification of the PD over the first set a class different from the class presented during the first classification.

In accordance with a fourth aspect of the disclosure, a PoE system comprises a PSE and a PD. The PD is configured to determine information on the type of the PSE based on output current of the PSE at a short circuit condition.

In accordance with a fifth aspect of the disclosure, a PoE system comprises a PD configured for performing a classification scheme to request a higher amount of power from a PSE and gradually reduce the requested amount of power if the request for power is denied by the PSE.

In accordance with a sixth aspect of the disclosure, a PoE system comprises a PD configured for performing a classification scheme to request a lower amount of power from a PSE and gradually increase the requested amount of power if the request for power is granted by the PSE.

In accordance with a seventh aspect of the disclosure, a PoE system comprises an integrated connector with PD circuitry provided inside the connector housing or attached to the housing.

In accordance with an eighth aspect of the disclosure, a PoE system comprises a PD detection mechanism for detecting a PD by determining the presence of one or more diodes in a device connected to the line. The PD detection mechanism detects the presence of the diodes based on an offset voltage in the current-voltage characteristics of the line.

In accordance with a ninth aspect of the disclosure, a PD comprises an active switch on the front end provided instead of or in parallel to a diode.

Additional advantages and aspects of the disclosure will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present disclosure are shown and described, simply by way of illustration of the best mode contemplated for practicing the present disclosure. As will be described, the disclosure is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the embodiments of the present disclosure can best be understood when read in conjunction with the following drawings, in which the features are not necessarily drawn to scale but rather are drawn as to best illustrate the pertinent features, wherein:

FIG. 1 is an exemplary diagram illustrating advanced PoE system.

FIG. 2 is a flow chart illustrating a procedure for setting different classes of an advanced PD on first and second 2-wire sets.

FIG. 3 is a flow chart illustrating a procedure for changing the class of an advanced PD presented on the first 2-wire set as the second 2-wire set is utilized for detection and classification.

FIG. 4 is a flow chart illustrating a procedure for changing the class of an advanced PD presented on the first 2-wire set when classification of the PD over the first 2-wire set is repeated.

FIG. 5 is a diagram illustrating measuring the PSE current limit during in-rush event.

FIG. 6 is a diagram illustrating measuring the PSE current limit after power-up event.

FIG. 7 is a flow chart illustrating a classification scheme for gradually reducing the amount of power requested by the PD.

FIG. 8 is a flow chart illustrating a classification scheme for gradually increasing the amount of power requested by the PD.

FIG. 9 illustrates an integrated LAN connector.

FIG. 10 illustrates an integrated LAN connector with PD circuitry placed inside the connector housing.

FIG. 11 illustrates an integrated LAN connector with PD circuitry coupled to the connector housing via a coupler.

FIG. 12 illustrates current-voltage characteristics of a line during a PD detection procedure.

FIG. 13 illustrates extrapolating the current-voltage characteristics to determine a voltage offset indicating the presence of one or more diode.

FIGS. 14 and 15 illustrate probing the line in a transient fashion to determine a voltage offset indicating the presence of one or more diode.

FIG. 16 schematically shows elements of a PD being detected.

FIG. 17 shows a conventional PD with diode bridges on its front end.

FIG. 18 illustrates a PD with active switches provided in parallel to diodes.

DETAILED DISCLOSURE OF THE EMBODIMENTS

The present disclosure will be made with the example of an advanced Power over Ethernet (PoE) system utilizing 4 pairs of wires for providing power from a Power Sourcing Equipment (PSE) to a Powered Device (PD). It will become apparent, however, that some concepts described herein are applicable to a PoE system utilizing any number of wires for providing power.

1) Setting Different Classes of Advanced PD on First and Second 2-Wire Sets

FIG. 1 is a simplified diagram illustrating an advanced Power over Ethernet (PoE) system 10 of the present disclosure. The advanced PoE system 10 comprises an advanced Power Sourcing Equipment (PSE) 12 and an advanced Powered Device (PD) 14 linked via 2-pair set 1 and 2-pair set 2. Each of the 2-pair sets 1 and 2 is composed of 2 pairs of wires arranged for providing power from the PSE 12 to PD 14. The advanced PSE 12 is configured to provide power to the PD 14 over 4 pairs of wire in the pair sets 1 and 2, whereas the advanced PD 14 is configured to receive power supplied over the 4 pairs of wire. One skilled in the art would understand that the advanced PSE 12 may be able to operate with a regular PD that receives power from only 2 pairs of wire. Similarly, the advanced PD 14 may be able to operate with a regular PSE that supplies power over only 2 pairs of wire.

As defined, for example, in the IEEE 802.3af standard, a PSE and a PD participate in a PD detection procedure, during which the PSE probes a link to detect the PD. If the PD is detected, the PSE checks the PD detection signature to determine whether it is valid or non-valid. While the valid PD detection signature indicates that the PD is in a state where it will accept power, the non-valid PD detection signature indicates that the PD is in a state where it will not accept power.

If the signature is valid, the PD has an option of presenting a classification signature to the PSE to indicate how much power it will draw when powered up. In accordance with the IEEE 802.3af standard, a PD may be classified as class 0 to class 4. A PD of class 1 requires that the PSE supplies at least 4.0 W, a PD of class 2 requires that the PSE supplies at least 7.0 W, and a PD of class 0, 3 or 4 requires at least 15.4 W. Based on the determined class of the PD, the PSE applies the required power to the PD. The advanced PSE 12 of the present disclosure may be a high-power PSE capable of providing higher power than the IEEE 802.3af standard requires.

In accordance with the present disclosure, the advanced PSE 12 and the advanced PD 14 may perform separate detection and classification procedures for 2-pair set 1 and 2-pair set 2. In particular, the first detection and classification procedure performed over the 2-pair set 1 may be followed by the second detection and classification procedure carried out over the 2-pair set 2.

As illustrated in FIG. 2, during the detection step 22, the PSE 12 may probe a link to the PD 14 over the 2-pair set 1 to detect the PD 14. If the PD 14 is detected, the PSE 12 may perform classification of the PD 14 during the classification step 24, for example, by applying classification voltage V_(Class) and measuring classification current I_(Class) using the 2-pair set 1. The classification current I_(Class) may represent the class of the PD 14. Thereafter, the PSE 12 may perform the detection procedure over the 2-pair set 2 (step 26), followed by the classification procedure over the 2-pair set 2 (step 28).

The PSE 12 may provide power to the PD 14 over the 2-pair set 1 and/or the 2-pair set 2 based on the first classification in step 24. Alternatively, power from the PSE 12 to the PD 14 may be supplied over the 2-pair set 1 and/or the 2-pair set 2 based on the first classification in step 24.

In accordance with an embodiment of the disclosure, the advanced PD 14 may be configured to present during the second classification in step 28 a class different from the class determined during the first classification in step 24. Hence, the classification procedure may be used to communicate to the PSE 12 any desired information. For example, if 5 classes 0 to 4 are used for classification, two classification procedures over 2-pair sets 1 and 2 may provide 5²=25 states of an information signal, each of which may represent a bit of information.

The advanced PD 14 may have circuitry for changing its class presented on the 2-pair set 1 and/or the 2-pair set 2 in response to a predetermined condition. For example, the class changing circuitry may control the classification current I_(Class) measured by the PSE 12 in response to the classification voltage V_(Class).

The advanced PSE 12 may be configured to recognize the information provided by the PD 14 during the classification steps 24 and 28. For example, a change in the class during the step 28 compared to the step 24 may indicate to the PSE 12 that the PD 14 communicates information. The PSE 12 may be configured to provide a response to the information from the PD 14. For example, this response may be represented by signals supplied by the PSE 12 during the detection procedure and/or classification procedure over the 2-pair set 1 and/or the 2-pair set 2.

2) Changing Class of Advanced PD Presented on First 2-Wire Set as Second 2-Wire Set is Utilized for Detection and Classification.

FIG. 3 illustrates another embodiment of the disclosure, in which the PSE 12 detects and classifies the PD 14 on the 2-pair set 1 (steps 32, 34). After this detection and classification procedure is completed, the PD 14 may present on the 2-pair set 1 a class different from the class initially determined by the PSE 12 (step 36) as the PSE 12 performs detection and classification of the PD 14 on the 2-pair set 1 (steps 38, 40). The different class on the same 2-pair set may indicate to the PSE 12 that both 2-pair sets 1 and 2 are connected to the same PD and may confirm 4-pair continuity. Power from the PSE 12 to the PD 14 may be supplied over the 2-pair set 1 and/or the 2-pair set 2 after completion of the classification on the 2-pair set 1 or classification on the 2-pair set 2.

3) Changing Class of Advanced PD Presented on First 2-Wire Set when Classification of PD Over First 2-Wire Set is Repeated.

A further embodiment of the disclosure enables the advanced PoE system 10 to convey additional information by using a classification scheme that toggles the class values between two or more classes. For example, as illustrated in FIG. 4, the PSE 12 may classify the PD 14 over the 2-pair set 1 (step 42). The PD 14 presents class X during this classification (step 44). The PSE 12 may record this class value. Then, the PSE 12 classifies the PD 14 over the 2-pair set 2 (step 46). The PD 14 may present either a different class value on the 2-pair set 2 to communicate desired information, as discussed above. Alternatively, the PD 14 may present the same class value X on the 2-pair set 2.

Thereafter, the PSE 12 may repeat classification of the PD 14 over the 2-pair set 1 (step 48). In response, to the second classification signal from the PSE 12 over the 2-pair set 1, the PD 14 may present a different classification value to provide the PSE 12 with additional information. The PSE 12 may perform further classification of the PD 14 over the 2-pair set 1 and/or the 2-pair set 2. The PD 14 may be configured to change the class value during the classification procedures.

For example, the advanced PD 14 may be provided with circuitry controlled to change the class value presented on the 2-pair set 1 and/or the 2-pair set 2 in response to a predetermined condition. Alternatively, the presented class value may be changed with time after the initial classification.

Besides enabling the PD 14 to supply additional information, this classification scheme allows the PSE 12 to determine that the 2-pair sets 1 and 2 are connected to an advanced PD. Also, the PSE 12 may confirm that there is continuity on both 2-pair sets.

4) Utilizing Current Limit for Conveying Information on PSE

In accordance with a further embodiment of the disclosure, the PD 14 is configured to determine a type of a PSE linked to the PD 14 based on output current I_(LIM) of the PSE during a short circuit condition. As illustrated in FIG. 5, the current I_(LIM) may be measured during an inrush event. The PD 14 contains a circuit 62 for measuring the current I_(LIM) and signal/logic conditioning. This circuit may be connected to the PD downstream electronics 64 using PD hot swap control 66.

Alternatively, as illustrated in FIG. 6, the PD 14 may measure the current I_(LIM) after the PD is powered up by applying a load. A switchable load 68 may be resistive, capacitive or active. The load 68 is switched on momentarily after capacitor C1 is charged up. Also, the load may be in a form of a voltage source.

By monitoring the port voltage or by presenting a voltage source as a load, the PD can prevent the PSE port voltage from dropping to a level at which the PD would be disconnected.

Based on the current I_(LIM), the PD 14 may determine whether the respective PSE is a device operating in accordance with the IEEE 802.3af standard, a high-power PSE capable of providing higher power than the IEEE 802.3af standard requires, or a legacy PSE. In particular, the value of the current I_(LIM) for an IEEE 802.3af device is in the range from 400 to 450 mA, a high-power PSE may have this current at a level of about 800 mA, and a legacy device may have the current I_(LIM) equal, for example, to about 200 mA.

If the PD 14 determines that the PSE is a legacy device, the PD 14 may determine additional information as to the type of this legacy device based on a particular value of the measured current I_(LIM).

5) Classification Scheme for Gradually Reducing the Amount of Power Requested by PD

FIG. 7 is a flow chart illustrating a further embodiment of the present disclosure provided to increase probability that a PD will be powered by a PSE. In particular, multiple PSEs may be combined in a multi-port PSE device that supplies power to multiple PDs. A multi-port PSE device typically uses a single power supply to convert AC line power to the 802.3 af compliant power that can be sent over the link to the PD. Therefore, there may be a competition for power among the links powered by PSEs. To address this problem, the IEEE 802.3af standard divides PDs into 5 classes based on their maximum power consumption. PD communicates its class to the PSE before the link is powered. If the power required by the PD's advertised class is more than power available from the PSE, the PSE denies the power request. In particular, PSE must supply at least 4.0 W to a link with a PD of class 1 connected to the link, at least 7.0 W to a link with a PD of class 2, and at least 15.4 W to a link with a PD of class 0, 3 or 4.

For example, if a 4-port PSE device is already powering 3 PDs of class 2, it must allocate 21 W for powering the respective 3 links. If the PSE device detects a PD on its last port, it must ensure that it has the capabilities to power that PD. For example, if a PSE device operates with a 25 W power supply, it has only 4 W left. Therefore, it cannot provide power to the fourth PD of class 2. However, a PSE device with a 30 W power supply can power the fourth PD of class 2 because it has 9 W left.

This example shows that a multi-port PSE device must keep account of the power demands from the links to compare the power demands with the capabilities of its power supply before powering a link. Typically, a PSE device is accompanied with a microcontroller and custom software to provide its power management.

In accordance with the present disclosure, the advanced PD 14 gradually reduces a requested power level if its initial request for power is denied. For example, in its initial request, the PD 14 may request class 3 power allocation (step 72) and determine whether its request is denied or granted (step 74). If this request is granted, the PSE 12 supplies the PD 14 with the requested power (step 76).

However, if the initial request is denied, the PD 14 may reduce the amount of requested power. For example, in the next request for power, the PD 14 may request class 2 power allocation (step 78) and determine whether this request is denied or granted (step 80). If this request is granted, the PSE 12 supplies the requested power to the PD (step 82).

If this request is also denied, the PD 14 may further reduce the amount of requested power. In particular, the PD may request class 1 power allocation (step 84). As a result, the PD 14 increases probability of obtaining power from the PSE 12.

6) Classification Scheme for Gradually Increasing the Amount of Power Requested by PD

Alternatively, instead of stepping down the classification power request, the PD 14 may start with a request for a low power level. For example, as illustrated in FIG. 8, the PD 14 may start with a request for class 1 power allocation (step 92), and determine whether this request is denied or granted (step 94). If this request is denied, the PD 4 may repeat its request later (step 96). If the request is granted, the PSE provides the PD 14 with requested power (step 98).

Then, the PD 14 may determine whether the supplied amount of power corresponds to a required amount of power (step 100). If so, it stops the classification procedure (step 102). However, if the supplied power is below the required level, the PD 14 may remove the supplied power (step 104) and issue a request for a higher power level. For example, the PD 14 may request class 2 power allocation (step 106). This procedure may continue to request class 3 allocation or further until the required power is provided or a request for power is denied.

To issue each request for power allocation, the PD 14 may initiate detection and classification procedures to present the respective class to the PSE 12. The procedures illustrated in FIGS. 7 and 8 may be implemented in any existing or yet to be defined PoE system that includes a system of graded power usage levels.

7) Integrated LAN Connector for PD

FIGS. 9, 10, and 11 illustrate an integrated LAN connector 110 that may be provided in a PoE system for supporting a PD. The connector may include current limit circuitry, signature providing circuitry or any other circuitry for supporting PoE operations, such as voltage regulators, filters, load balancing circuitry, etc.

As shown in FIG. 10, the PD circuitry may be provided inside the housing of the LAN connector 110. Alternatively, as shown in FIG. 11, the PD circuitry may be attached to the connector housing via a coupler. The connector 110 may support 10, 100 and 1000base T communications protocols.

8) Detecting PD by Looking for Diode Bridge

In accordance with another embodiment of the present disclosure, an advanced PoE system comprises a PD detecting mechanism for gathering information about a device linked to a PSE, and detecting a PD using the current-voltage (IV) characteristics of the line between the PSE and this device.

The PD requesting power may contain one or more diodes in a series connection. The PD detecting mechanism of the present disclosure may determine the IV characteristics of the line to detect the presence of the diode or diodes in the series connection. A voltage offset on the IV curve may be used to determine that the device connected to the line contains the diode or diodes in the series connection. If the diode or diodes are detected, the PD detection mechanism may conclude that the device connected to the line is a PD.

FIG. 12 illustrates an exemplary IV characteristics of the line during a conventional PD detection procedure using a signature resistance defined in the IEEE 802.3af standard. A signature resistance of a PD may be determined as ${R = \frac{{V\quad 2} - {V\quad 1}}{{I\quad 2} - {I\quad 1}}},$ where I1 and I2 are current values measured in response to the respective voltage values V1 and V2 applied to the line.

In accordance with an embodiment of the present disclosure, a voltage offset that indicates the presence of the diode or diodes in the series connection may be detected by extrapolating the IV characteristics of the line, as illustrated in FIG. 13.

Alternatively, a voltage offset indicating the presence of the diode or diodes in the series connection may be determined by probing the line in a transient fashion with a low duty cycle. As illustrated in FIG. 14, gradually reducing voltage probe values V1, V2, V3 and V4 may be asserted onto the line with a low duty cycle. As shown in FIG. 15, current values I1, I2, I3 and I4 are measured in response to the respective voltage probe values.

FIG. 15 schematically illustrates a PD connected to the line. The PD includes diodes D1, D2, a series capacitor C_(IN) and a series load transistor R_(LOAD). A low duty cycle of the voltage probe sequence is provided to prevent a series capacitor C_(IN) from charging up, which would result in corrupting the measurement of the current. Also, this method of determining the offset voltage prevents the series load transistor R_(LOAD) from influencing the current measurement.

As discussed above, a voltage source may be used for probing the line. Alternatively, a current source or a resistive source may be applied to the line.

9) Use of Active Switching Element on PD Front End

As illustrated in FIG. 17, a conventional PD may have one or more diodes or a diode bridge such as a diode bridge BR1 or BR2 provided on a PD front end between a PD interface for supporting PoE connections to the PSE, and a PoE interface controller, such as the LTC®4257 controller developed by Linear Technology Corporation for providing a power interface port for a PD. These diodes cause a loss in power.

In accordance with an embodiment of the present disclosure, the diodes on the PD front end may be replaced with active switching elements to reduce power consumption. Switching devices, such as NMOS, PMOS devices or relays may be used instead of passive diodes. Also, a combination of these device may be used.

Alternatively, as illustrated in FIG. 18, the switching elements may be placed in parallel with respective diodes.

If a MOS device is utilized, a body diode may be used to conduct current before the MOS device is turned on. Further, MOS body diodes may be used to allow detection and classification of the PD to occur before turning on an active switch.

The foregoing description illustrates and describes aspects of the present invention. Additionally, the disclosure shows and describes only preferred embodiments, but as aforementioned, it is to be understood that the invention is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein, commensurate with the above teachings, and/or the skill or knowledge of the relevant art.

The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the invention.

Accordingly, the description is not intended to limit the invention to the form disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments. 

1. A Power over Ethernet (PoE) system comprising a Power Sourcing Equipment (PSE) and a Powered Device (PD) configured for interacting over a first 2-pair set of wires and a second 2-pair set of wires provided for supplying power from the PSE to the PD; the PSE and the PD being configured to perform separate PD classification procedures over the first and the second 2-pair sets to support PoE operations that are not defined by the IEEE 802.3af standard.
 2. The system of claim 1, wherein the PSE is configured to perform first classification of the PD over the first set, followed by second classification of the PD performed over the second set, and the PD is configured to present a class during the second classification different from the class presented during the first classification.
 3. The system of claim 1, wherein the PSE and the PD are configured to perform first classification of the PD over the first set and second classification of the PD over the second set, and the PD is configured to present on the first set a class different from the class presented during the first classification as the second classification of the PD is performed over the second set.
 4. The system of claim 1, wherein the PSE and the PD are configured to perform first classification of the PD over the first set, followed by second classification of the PD performed over the second set, and the PD is configured to present during a further classification of the PD over the first set a class different from the class presented during the first classification.
 5. The system of claim 1, wherein the PD is configured to determine information on a type of the PSE based on output current of the PSE at short circuit condition.
 6. The system of claim 1, wherein the PD is configured for performing a classification scheme to request a higher amount of power from a PSE and gradually reduce the requested amount of power if the request for power is denied by the PSE.
 7. The system of claim 1, wherein the PD is configured for performing a classification scheme to request a lower amount of power from a PSE and gradually increase the requested amount of power if the request for power is granted by the PSE.
 8. The system of claim 1 further comprising an integrated connector having a housing configured for accommodating circuitry of the PD inside the connector.
 9. The system of claim 1 further comprising an integrated connector including a coupler for attaching circuitry of the PD to the connector.
 10. A PoE system comprising a PD detection mechanism for detecting a PD by determining presence of one or more diodes in a device connected to a PSE via a line, the PD detection mechanism is configured for detecting presence of the diodes based on an offset voltage in current-voltage characteristics of the line.
 11. A PoE system having a PD interface for supporting PoE connection of a PD to a PSE, and a PoE interface controller for providing a power interface port for the PD, circuitry including active switching elements being connected between the interface and the controller. 